To add here, FEBuilder is as close to an “all in one” software you can use to get into making a hack. It’ll be easier to use than Nightmare/FEditor as well. FE8 is now considered easier to hack and is the primary GBA ROM used today for hacking. Would recommend you try that instead of FE7 if this is your first rodeo.
Here’s the FEBuilder thread: FE_Builder_GBA
I’d recommend you also join the discord server since there’s a help channel there and usually active discussion, so you can get answers quickly when you find yourself stuck.
Good luck!